概括的描述一下Spring注册流程

Spring经过大神们的构思、编码，日积月累而来，所以，对其代码的理解也不是一朝一夕就能快速完成的。源码学习是枯燥的，需要坚持！坚持！坚持！当然也需要技巧，第一遍学习的时候，不用关注全部细节，不重要的代码可以先忽略掉，达到理解大体的架子及流程，避免第一次就陷入某个坑里出不来。第二遍针对某个流程更深入的、有针对性的去分析学习，当然遇到某个实在过不去的坎可以标记，后面再思考，毕竟是别人设计的，有些不是那么容易理解，可以使用google，次数多了，总会有收获！

概括的描述一下Spring背后的操作，解析applicationgContext.xml，将xml中定义的bean(如loginService和loginResource)解析成Spring内部的BeanDefinition，并以beanName(如loginService)为key，BeanDefinition(如loginService相应的BeanDefinition)为value存储到DefaultListableBeanFactory中的beanDefinitionMap(其实就是一个ConcurrentHashMap)中，同时将beanName存入beanDefinitionNames(List类型)中，然后遍历beanDefinitionNames中的beanName，进行bean的实例化并填充属性，在实例化的过程中，如果有依赖没有被实例化将先实例化其依赖，然后实例化本身，实例化完成后将实例存入单例bean的缓存中，当调用getBean方法时，到单例bean的缓存中查找，如果找到并经过转换后返回这个实例(如LoginResource的实例)，之后就可以直接使用了。

上边提到在Spring容器启动的过程中，会将Bean解析成Spring内部的BeanDefinition结构，BeanDefinition的内部结构。直接看BeanDefinition源码

  1. public interface BeanDefinition extends AttributeAccessor, BeanMetadataElement {
  2. /**
  3. * Scope identifier for the standard singleton scope: "singleton".
  4. * <p>Note that extended bean factories might support further scopes.
  5. */
  6. String SCOPE_SINGLETON = ConfigurableBeanFactory.SCOPE_SINGLETON;
  7. /**
  8. * Scope identifier for the standard prototype scope: "prototype".
  9. * <p>Note that extended bean factories might support further scopes.
  10. */
  11. String SCOPE_PROTOTYPE = ConfigurableBeanFactory.SCOPE_PROTOTYPE;
  12. /**
  13. * Role hint indicating that a {@code BeanDefinition} is a major part
  14. * of the application. Typically corresponds to a user-defined bean.
  15. */
  16. int ROLE_APPLICATION = 0;
  17. /**
  18. * Role hint indicating that a {@code BeanDefinition} is a supporting
  19. * part of some larger configuration, typically an outer
  20. * {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
  21. * {@code SUPPORT} beans are considered important enough to be aware
  22. * of when looking more closely at a particular
  23. * {@link org.springframework.beans.factory.parsing.ComponentDefinition},
  24. * but not when looking at the overall configuration of an application.
  25. */
  26. int ROLE_SUPPORT = 1;
  27. /**
  28. * Role hint indicating that a {@code BeanDefinition} is providing an
  29. * entirely background role and has no relevance to the end-user. This hint is
  30. * used when registering beans that are completely part of the internal workings
  31. * of a {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
  32. */
  33. int ROLE_INFRASTRUCTURE = 2;
  34. /**
  35. * Return the name of the parent definition of this bean definition, if any.
  36. */
  37. String getParentName();
  38. /**
  39. * Set the name of the parent definition of this bean definition, if any.
  40. */
  41. void setParentName(String parentName);
  42. /**
  43. * Return the current bean class name of this bean definition.
  44. * <p>Note that this does not have to be the actual class name used at runtime, in
  45. * case of a child definition overriding/inheriting the class name from its parent.
  46. * Hence, do <i>not</i> consider this to be the definitive bean type at runtime but
  47. * rather only use it for parsing purposes at the individual bean definition level.
  48. */
  49. String getBeanClassName();
  50. /**
  51. * Override the bean class name of this bean definition.
  52. * <p>The class name can be modified during bean factory post-processing,
  53. * typically replacing the original class name with a parsed variant of it.
  54. */
  55. void setBeanClassName(String beanClassName);
  56. /**
  57. * Return the factory bean name, if any.
  58. */
  59. String getFactoryBeanName();
  60. /**
  61. * Specify the factory bean to use, if any.
  62. */
  63. void setFactoryBeanName(String factoryBeanName);
  64. /**
  65. * Return a factory method, if any.
  66. */
  67. String getFactoryMethodName();
  68. /**
  69. * Specify a factory method, if any. This method will be invoked with
  70. * constructor arguments, or with no arguments if none are specified.
  71. * The method will be invoked on the specified factory bean, if any,
  72. * or otherwise as a static method on the local bean class.
  73. * @param factoryMethodName static factory method name,
  74. * or {@code null} if normal constructor creation should be used
  75. */
  76. void setFactoryMethodName(String factoryMethodName);
  77. /**
  78. * Return the name of the current target scope for this bean,
  79. * or {@code null} if not known yet.
  80. */
  81. String getScope();
  82. /**
  83. * Override the target scope of this bean, specifying a new scope name.
  84. */
  85. void setScope(String scope);
  86. /**
  87. * Return whether this bean should be lazily initialized, i.e. not
  88. * eagerly instantiated on startup. Only applicable to a singleton bean.
  89. */
  90. boolean isLazyInit();
  91. /**
  92. * Set whether this bean should be lazily initialized.
  93. * <p>If {@code false}, the bean will get instantiated on startup by bean
  94. * factories that perform eager initialization of singletons.
  95. */
  96. void setLazyInit(boolean lazyInit);
  97. /**
  98. * Return the bean names that this bean depends on.
  99. */
  100. String[] getDependsOn();
  101. /**
  102. * Set the names of the beans that this bean depends on being initialized.
  103. * The bean factory will guarantee that these beans get initialized first.
  104. */
  105. void setDependsOn(String... dependsOn);
  106. /**
  107. * Return whether this bean is a candidate for getting autowired into some other bean.
  108. */
  109. boolean isAutowireCandidate();
  110. /**
  111. * Set whether this bean is a candidate for getting autowired into some other bean.
  112. */
  113. void setAutowireCandidate(boolean autowireCandidate);
  114. /**
  115. * Return whether this bean is a primary autowire candidate.
  116. * If this value is true for exactly one bean among multiple
  117. * matching candidates, it will serve as a tie-breaker.
  118. */
  119. boolean isPrimary();
  120. /**
  121. * Set whether this bean is a primary autowire candidate.
  122. * <p>If this value is true for exactly one bean among multiple
  123. * matching candidates, it will serve as a tie-breaker.
  124. */
  125. void setPrimary(boolean primary);
  126. /**
  127. * Return the constructor argument values for this bean.
  128. * <p>The returned instance can be modified during bean factory post-processing.
  129. * @return the ConstructorArgumentValues object (never {@code null})
  130. */
  131. ConstructorArgumentValues getConstructorArgumentValues();
  132. /**
  133. * Return the property values to be applied to a new instance of the bean.
  134. * <p>The returned instance can be modified during bean factory post-processing.
  135. * @return the MutablePropertyValues object (never {@code null})
  136. */
  137. MutablePropertyValues getPropertyValues();
  138. /**
  139. * Return whether this a <b>Singleton</b>, with a single, shared instance
  140. * returned on all calls.
  141. */
  142. boolean isSingleton();
  143. /**
  144. * Return whether this a <b>Prototype</b>, with an independent instance
  145. * returned for each call.
  146. */
  147. boolean isPrototype();
  148. /**
  149. * Return whether this bean is "abstract", that is, not meant to be instantiated.
  150. */
  151. boolean isAbstract();
  152. /**
  153. * Get the role hint for this {@code BeanDefinition}. The role hint
  154. * provides the frameworks as well as tools with an indication of
  155. * the role and importance of a particular {@code BeanDefinition}.
  156. */
  157. int getRole();
  158. /**
  159. * Return a human-readable description of this bean definition.
  160. */
  161. String getDescription();
  162. /**
  163. * Return a description of the resource that this bean definition
  164. * came from (for the purpose of showing context in case of errors).
  165. */
  166. String getResourceDescription();
  167. /**
  168. * Return the originating BeanDefinition, or {@code null} if none.
  169. * Allows for retrieving the decorated bean definition, if any.
  170. * <p>Note that this method returns the immediate originator. Iterate through the
  171. * originator chain to find the original BeanDefinition as defined by the user.
  172. */
  173. BeanDefinition getOriginatingBeanDefinition();
  174. }


可以看到上面的很多属性和方法都很熟悉，例如类名、scope、属性、构造函数参数列表、依赖的bean、是否是单例类、是否是懒加载等，其实就是将Bean的定义信息存储到这个BeanDefinition相应的属性中，后面对Bean的操作就直接对BeanDefinition进行，例如拿到这个BeanDefinition后，可以根据里面的类名、构造函数、构造函数参数，使用反射进行对象创建。BeanDefinition是一个接口，是一个抽象的定义，实际使用的是其实现类，如ChildBeanDefinition、RootBeanDefinition、GenericBeanDefinition等。BeanDefinition继承了AttributeAccessor，说明它具有处理属性的能力；BeanDefinition继承了BeanMetadataElement，说明它可以持有Bean元数据元素，作用是可以持有XML文件的一个bean标签对应的Object。

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原文地址：https://www.cnblogs.com/yibutian/p/9588036.html